This invention relates to polyurethane-backed substrates, and to a process and composition for making same.
Carpets and other substrates having attached polyurethane foam layers are well-known and described, for example, in U.S. Pat. Nos. 3,755,212, 3,821,130, 3,862,879, 4,022,941, 4,171,395, 4,278,482, 4,286,003, 4,405,393, 4,483,894, 4,512,831, 4,515,646, 4,595,436, 4,611,044, 4,657,790, 4,696,849, 4,853,054, and 4,853,280. In commercial practice, these polyurethane-backed materials have been prepared from polyurethane-forming compositions based on toluene diisocyanate (TDI). However, for handling reasons, it is desired to substitute a diphenylmethane diisocyanate-based material for the TDI in this application.
TDI-based frothed polyurethanes have an excellent balance of physical properties, including good tensile strength, load bearing, tear strength and resiliency. Previous attempts to duplicate these properties with MDI-based systems failed to achieve this excellent balance. Generally, the MDI systems yield inferior resiliency when formulated to provide load-bearing, tensile, tear and elongation properties equivalent to those provided by TDI-based systems. Resiliency can be improved in these systems, typically by reduction of hard segment levels (decreased use of chain extender), but with this reduction comes a loss of tensile, tear, load-bearing and elongation.